The high spectral resolution of SPIRE is used to place limits on the presence of PH₃ in Saturn’s stratosphere. Using the best-fitting parameterised profiles from Fig. 6, we apply upper-level cutoffs between 1 mbar and 300 mbar and test the change in χ². The upper panels show the data (points) compared to models with high-altitude cut offs at different pressure levels (key shown in mbar in the upper left panel). The lower panels show Δχ² for the variable cutoff pressure with 1σ and 3σ confidence limits as the dotted horizontal lines.